Freed victims of human trafficking are to be given the right to stay in Britain for at least 30 days, the government announced today.

The Home Office is to sign a European convention designed to give victims, such as women sold into the sex trade, time to recover and decide whether they will help police prosecute their traffickers.

It has also published a national action plan to tackle trafficking with the Scottish Executive, which will involve posting specialist teams at UK ports and set up a telephone helpline for social workers, police and immigration staff who come into contact with victims.

The announcements came as the Crown Prosecution Service today revealed that "slave auctions" of trafficked women sold into prostitution are being staged on the concourses of British airports.

There were an estimated 4,000 victims of trafficking working in prostitution in the UK during 2003. It is believed the problem has grown since then. Another estimate put the figure at 10,000 in London and the Midlands alone.

However there were only 30 convictions for trafficking offences during 2004-06, according to figures gathered by the Conservatives in January.

Ministers previously refused to sign the European Convention on Action Against Trafficking in Human Beings, due to come into force next year, claiming it could be abused by illegal immigrants.

The decision is likely to win cross-party backing as the Conservatives urged ministers to sign the convention earlier this year.

Shadow home secretary, David Davis, said the step was vital for "moral reasons" in a bid to protect exploited victims, some of who are forced to have sex with up to 40 men a day.

Despite his party's previous opposition to signing the convention, Mr Davis said he was confident it would not attract more immigrants to Britain.

The announcement that the Home Office is to sign the convention was welcomed by ECPAT (End Child Prostitution, Child Pornography and the Trafficking of Children for Sexual Purposes) a coalition of children's charities and anti-slavery campaigners.

But the campaign group said child victims of trafficking would not be properly protected until the government gave them the right to residency.

ECPAT said the government's reservation on the UN Convention on the Rights of the Child restricted the human rights of children who have entered the country illegally, including those trafficked.

Christine Beddoe, director of ECPAT UK, said trafficked children and unaccompanied asylum seekers were currently returned to their home countries even when their family's whereabouts were unknown.

Ms Beddoe said: "The reservation is completely unacceptable and must be removed. It undermines the principle of the best interest of the child and all other efforts to combat child trafficking."